What Happens When SO2 Reacts With Steel?

Steel can be corroded by sulphur dioxide in the presence of water.
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Sulphur dioxide, SO2, is a colorless gas that is toxic to human beings. It is produced both naturally by volcano's and by combustion of car gasoline. In its pure form, sulphur dioxide does not react strongly with metal alloys such as steel. However, in the presence of defects and water, sulphur dioxide can be highly corrosive.

Reaction Between Sulphur Dioxide and Steel

Steel is a general term for metal alloys containing iron, carbon and manganese with smaller amounts of silicon, phosphorus, sulphur and oxygen. In the absence of water, sulphur dioxide does not react strongly with steel. However, if sulphur dioxide is exposed to the atmosphere it reacts with water vapor and oxygen forming corrosive sulphuric acid. This substance is highly corrosive and can damage steel.